1. Field of the Invention
The present invention relates to an image forming system wherein an electrostatic latent image is formed on an image bearing member and then is developed, and a process cartridge including the image bearing member and a developing device therein and removably mountable on the image forming system.
2. Related Background Art
In an image forming system such as an electrophotographic system and the like, in order to keep constant a distance between an image bearing member and a developer bearing member for supplying developer to the image bearing member, spacers formed on a developing device are abutted against the image bearing member. More particularly, the developing device is pivotally mounted on a shaft, and the spacers are urged against the image bearing member by utilizing a moment generated around the shaft due to the gravity force acting on the developing device.
In such an image forming system, if the gravity force (weight) of the developing device is increased, the urging force of the spacers against the image bearing member will also increase, thereby damaging the image bearing member and(or) spacers.
Recently, image forming systems wherein a process cartridge including an image bearing member and a developing device supported by a common supporting means is removably mounted on the image forming system have widely been used.
In such a process cartridge, as the service life of the image bearing member is extended, the capacity of the developer container of the developing device has been increased. However, when the capacity of the developer container of the developing device is increased, the weight of the developing device is also increased, thus causing the above problem. Consequently, the process cartridge inconvenient must be exchanged for a new one (due to the damage of its image bearing memebr and(or) spacers) even when the photosensitivity of the image bearing member is not yet deteriorated and an adequate amount of developer still remains within the developing device.
Further, since the above-mentioned common supporting means of the process cartridge is generally molded from synthetic resin, the mechanical rigidity thereof is so small as to easily deform the supporting means. Further, in general, a gear for transmitting a rotational driving force to the developer bearing member is disposed at one of the longitudinal sides of the developing device. In this case, when a driving force is applied to the gear, a greater load acts on that one longitudinal side of the developing device in comparison with the other longitudinal side of the developing device, thus torsionally deforming the supporting means. Such torsional deformation of the supporting means is inconvenient in that the urging force of the spacers against the image bearing member at one longitudinal side of the developing device differs from the urging force at the other longitudinal side of the developing device, thereby causing a difference in the density of the image developed on the image bearing member from the one side (left) to the other side (right).